In optical networks, multiple wavelengths of light are used to support multiple communications channels on a single fiber. Optical amplifier spans are used in such networks to amplify optical signals that have been subject to attenuation over multi-kilometer fiber-optic links. A typical amplifier span may include erbium-doped fiber amplifier components that are pumped with diode lasers. Amplifiers have also been studied that use diode-laser pumping to generate gain through stimulated Raman scattering. Optical amplifiers based on erbium-doped fibers and Raman pumping increase the strength of the optical signals being transmitted over the fiber-optic links.
Sometimes channels in a communications link may be abruptly added or dropped. Channels may be dropped due to an accidental fiber cut. Channels may also be added or dropped suddenly due to a network reconfiguration. When the number of channels carried by a transmission fiber span changes abruptly, the total signal power being transported over the span also changes suddenly. If a Raman amplifier span is pumped at a constant power, these sudden changes in signal power will result in transient effects in the gain of the Raman amplifier. Gain transients cause fluctuations in the power of the output signals from the amplifier. Output signals that are too weak may be difficult to detect without errors. Output signals that are too strong may give rise to nonlinear optical effects in fiber.